Installing Hot Tub

Hello,

I have a couple questions about installing a hot tub in our back yard.
I have to run about 45 feet of cable indoors from the primary breaker panel to the outside wall where it will connect to the subpanel GFCI shutoff on the outside of the house.
When the cable comes out of the house it will be low to the ground, so, can't go directly into the back of that subpanel, I will do conduit from where it comes up, and up to the panel. My question is can I use romex/NMD90 6/3 for this? I know romex is acceptable for indoors, and into the back of the panel. But, since mine has to come out of the house in conduit and up about 2 feet to the subpanel on the outside wall, is this okay? If not, what would you guys recommend?
Then from the GFCI outside panel, I'll use THHN in conduit or direct bury cable to the hot tub.

Thanks,
Justin.

 

The NEC doesn't allow it and I suspect the CEC doesn't either, but I am not that familiar with the CEC.

Be sure the THHN is dual rated THHN/THWN. I wouldn't use cable.